The invention relates to a wire-type electric discharge machining method and apparatus capable of reliably removing cores of large size or complicated shape from a workpiece.
FIG. 8 shows a conventional electric discharge machining apparatus equipped with a core removing unit. In this drawing, labelled at 1 is the wire electrode, 2 is the work to be machined, 3 is a table movable in an X-Y plane on which the work 2 is mounted and secured, 4 is an X-axis motor for driving the table 3 in the X direction, 5 is a Y-axis motor for driving the table 3 in the Y direction, 6 is a numerical control unit for, inter alia, actuating the X-axis motor 4 and the Y-axis motor 5 to move the table 3 with respect to the wire electrode 1, 7 is the machining power source for supplying machining current to the gap between the wire electrode 1 and the work 2, and 8 is a core removing unit for removing the core 9 cut from the work 2 by the wire electrode 1.
FIG. 9 shows the main mechanical elements of the core removing unit 8. In this drawing, 10 is a suction head for attracting the core 2. The suction head 10 is secured to one end of a horizontal arm 11, the other end of which is rotatably attached via a bearing 12 to the lower end of an unloading shaft 13. The shaft 13 is made vertically movable with the aid of a mechanism not shown. An upper nozzle 14 supplies machining liquid from above to a machining zone between the wire electrode 1 and the work 2, this upper nozzle 14 being secured to a bracket 16 capable of vertical movement. Lower nozzle 15 supplies machining liquid from below the work 2 to the machining zone, this lower nozzle 15 being secured to a fixed bracket 16.
FIG. 10 shows the work 2 in plan view. In this drawing, 17, 18, 19 and 20 are various contours to be machined by the wire electrode 1, and 21, 22, 23 and 24 are the starting holes through which the wire electrode 1 will be passed.
The operation of this system will now be described. Upon application of a machining voltage from power source 7 across the wire electrode 1 and the work 2, an electric spark is generated in the machining gap formed between them. The X-axis motor 4 and the Y-axis motor 5 are driven in accordance with signals from the numerical control unit 6 so that the table 3 is moved along a given contour, whereby machining is performed. After the completion of machining, the core 9 is removed from the work 2 and taken out.
The process of machining the work 2 into a given shape will now be described.
To machine the contour 17 shown in FIG. 10, the wire electrode 1 is passed through the starting hole 21, machining liquid (not shown) is jetted from the upper nozzle 14 and the lower nozzle 15 to the gap between the wire electrode 1 and the work 2, and the machining voltage is applied across the wire electrode 1 and the work 2 to generate electric discharge.
Under the foregoing conditions, the work 2 is moved such that the trace of the wire electrode 1 advances from the starting hole 21 in the direction of the arrows shown in the drawing, whereby the work 2 is machined so as to have contour 17.
Upon completion of machining corresponding to the contour 17, the core 9 defined by the contour 17 is separated as shown in FIG. 9 while being supported by the lower nozzle 15.
Then, as shown in FIG. 9, the upper nozzle 14 and the bracket 16 thereof are retracted upwardly, and the suction head 10 is positioned in the space between the upper nozzle 14 and the work 2.
That is, the unloading shaft 13 is lowered close to the work 2, the arm 11 is turned, the suction head 10 is positioned (according to positioning information from the numerical controller 6) so as to face the upper side of the core 9, and the suction head 10 is attached to the core 9. The unloading shaft 13 and the suction head 10 are then moved up so that the core 9 is lifted up above the work 2. Then, upon turning the arm 11, the core 9 is moved away from the work 2, and the suction force of the suction head 10 is released, so that the core 9 is disposed of.
Thereafter, machining for the next contour is begun.
Where various contours as shown in FIG. 10 are to be machined, after the contour 17 is subjected to machining and the core 9 is automatically removed, the wire electrode 1 is automatically passed through the starting hole 22, the contour 18 is machined in the same manner as the contour 17, and its core 9 is automatically removed by the core removing unit 8.
Thereafter, in this way, each core 9 is automatically removed by the core removing unit 8; as a result, all the contours 17, 18, 19 and 20 are machined.
With the conventional wire electrospark machining apparatus composed as described above, the core 9 is attracted by the suction head 10, lifted above the work 2, and then taken out. However, the space between the work 2 and the upper nozzle 14 cannot be made large; contrarily, the core removing unit 8 inclusive of the suction head 10 and the arm 11 must be made small in size; thus, the cores which can be removed are limited in both size and weight. For example, a large core having a contour such as at 18 in FIG. 10 cannot be removed automatically, and cores of long and complicated shape such as at 20 tend to interfere with the work 2 when being attracted and lifted, thereby making automatic removal impossible. That is, cores which can be automatically removed are limited. In this example, only the cores of contours 17 and 19 can be removed automatically. Thus, the contours which can be subjected to continuous automatic machining are still limited.